Improved plant availability by advanced condition based inspections

Abstract

An industrial plant has to operate safely, reliably and efficiently at the lowest possible cost. Plant availability plays an important role regarding economic life optimisation. Industrial installations that are under pressure and are operating at high temperatures have a limited life due to creep and fatigue. It is, therefore, of critical importance to know the location of any possible weak spots in the installation. To avoid safety risks, unplanned plant shutdown and, as a consequence, high costs for unavailability, cycling and repair, periodic inspections and strain measurements are recommended. A Speckle Image Correlation Analysis (SPICA) system enables on-stream measurement of deformation due to creep in critical areas like the heat-affected zone in welds. Plant management and operators use the strain measurements to take action when necessary and, consequently, prevent failures. In those plants that have been provided with SPICA-technology for some years plant availability has improved significantly as a result. Another important development for yielding improved availability concerns steam drums. During some 20 years, KEMA has been performing automated ultrasonic steam drum inspections from outside. The Dutch authorities accepted this methodology in this period as an alternative (rather than an addition) after several pilot projects. An advantage of this inspection methodology is the possibility to record of the inspection results and possibility of thus trending these data. The resulting reduction of through time appeared a major benefit for plant owners. Since the authorities adopted the RBI approach during the last 10 years, another advantage of the inspection methodology became apparent: complete scanning and recording of the inspection data of circumferential and longitudinal (butt and fillet) welds, inspection of nozzle welds and inner radius as well as corrosion mapping has been covering all higher risk areas in these drums. This enhanced inspection programme together with improved monitoring of operation parameters during operation has resulted in dramatic inspection interval extension. This attractive method for inspection interval extension has been applied at several Dutch power plants.